Revert "[GN] Remove a duplication of a source type check"

This reverts commit 844a031c63c6ec1123da1b5b0caa97958679ddf5.

Reason for revert: This CL causes failures when generating Xcode project on iOS platform, please see comments inline.

Original change's description:
> [GN] Remove a duplication of a source type check
> 
> There was a duplication of the source type checking. It may lead
> errors when a type set will be changed for a language.
> 
> R=​dpranke@chromium.org
> 
> Bug: None
> Change-Id: Ieab8885899446e625cfe20c1650418a085b937ee
> Reviewed-on: https://chromium-review.googlesource.com/702414
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>
> Commit-Queue: Dirk Pranke <dpranke@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#506763}

TBR=dpranke@chromium.org,vladbelov@yandex-team.ru

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: None
Change-Id: I5dd0a68f9dd9ac1edd6b94e248bdf5959f83b3ab
Reviewed-on: https://chromium-review.googlesource.com/747087
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#512888}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 8db77a10a3b90ef4f079ca1442cd9f6064ad214f
1 file changed
tree: 489c720fab7ca5296bc80a43fce26e58e562c073
  1. tools/